Reflective and transflective liquid crystal displays (LCDs) have been extensively used in personal information display because of their many advantages including low power consumption and light weight. In most reflective and transflective direct-view devices, however, an achromatic quarter-wave retardation film is required to provide a good dark state and high contrast ratio.
The combination of a chromatic half-wave film and a chromatic quarter-wave film at a specific angle has been commonly used for broadband quarter-wave film applications. See for example, S. Pancharatnam, Proceedings of the Indian Academy of Science, Section A, Vol. 41, 130 (1955); and T. H Yoon, G. D. Lee and J. C. Kim, Opt. Lett., Vol. 25, 1547 (2000). This combination fabrication method is rather simple, but the spectral bandwidth is insufficient for a full color display. Recently, Zhu et al filed a U.S. provisional patent application (60/419,181) on this approach in which a broadband quarter-wave film is realized with the combination of a half-wave film and a TN-LC film in a specific configuration. The result is a spectral bandwidth has been largely improved, but is still inadequate, especially in the blue and red regions.
It remains necessary to provide a quarter-wave film with much wider bandwidth for useful full color flat panel displays.